trailer: process trailers from input message and arguments

Implement the logic to process trailers from the input message
and from arguments.

At the beginning trailers from the input message are in their
own "in_tok" doubly linked list, and trailers from arguments
are in their own "arg_tok" doubly linked list.

The lists are traversed and when an "arg_tok" should be "applied",
it is removed from its list and inserted into the "in_tok" list.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

trailer.c

@@ -67,3 +67,213 @@ static int same_trailer(struct trailer_item *a, struct trailer_item *b)
 {
 	return same_token(a, b) && same_value(a, b);
 }
+
+static void free_trailer_item(struct trailer_item *item)
+{
+	free(item->conf.name);
+	free(item->conf.key);
+	free(item->conf.command);
+	free((char *)item->token);
+	free((char *)item->value);
+	free(item);
+}
+
+static void update_last(struct trailer_item **last)
+{
+	if (*last)
+		while ((*last)->next != NULL)
+			*last = (*last)->next;
+}
+
+static void update_first(struct trailer_item **first)
+{
+	if (*first)
+		while ((*first)->previous != NULL)
+			*first = (*first)->previous;
+}
+
+static void add_arg_to_input_list(struct trailer_item *on_tok,
+				  struct trailer_item *arg_tok,
+				  struct trailer_item **first,
+				  struct trailer_item **last)
+{
+	if (after_or_end(arg_tok->conf.where)) {
+		arg_tok->next = on_tok->next;
+		on_tok->next = arg_tok;
+		arg_tok->previous = on_tok;
+		if (arg_tok->next)
+			arg_tok->next->previous = arg_tok;
+		update_last(last);
+	} else {
+		arg_tok->previous = on_tok->previous;
+		on_tok->previous = arg_tok;
+		arg_tok->next = on_tok;
+		if (arg_tok->previous)
+			arg_tok->previous->next = arg_tok;
+		update_first(first);
+	}
+}
+
+static int check_if_different(struct trailer_item *in_tok,
+			      struct trailer_item *arg_tok,
+			      int check_all)
+{
+	enum action_where where = arg_tok->conf.where;
+	do {
+		if (!in_tok)
+			return 1;
+		if (same_trailer(in_tok, arg_tok))
+			return 0;
+		/*
+		 * if we want to add a trailer after another one,
+		 * we have to check those before this one
+		 */
+		in_tok = after_or_end(where) ? in_tok->previous : in_tok->next;
+	} while (check_all);
+	return 1;
+}
+
+static void remove_from_list(struct trailer_item *item,
+			     struct trailer_item **first,
+			     struct trailer_item **last)
+{
+	struct trailer_item *next = item->next;
+	struct trailer_item *previous = item->previous;
+
+	if (next) {
+		item->next->previous = previous;
+		item->next = NULL;
+	} else if (last)
+		*last = previous;
+
+	if (previous) {
+		item->previous->next = next;
+		item->previous = NULL;
+	} else if (first)
+		*first = next;
+}
+
+static struct trailer_item *remove_first(struct trailer_item **first)
+{
+	struct trailer_item *item = *first;
+	*first = item->next;
+	if (item->next) {
+		item->next->previous = NULL;
+		item->next = NULL;
+	}
+	return item;
+}
+
+static void apply_arg_if_exists(struct trailer_item *in_tok,
+				struct trailer_item *arg_tok,
+				struct trailer_item *on_tok,
+				struct trailer_item **in_tok_first,
+				struct trailer_item **in_tok_last)
+{
+	switch (arg_tok->conf.if_exists) {
+	case EXISTS_DO_NOTHING:
+		free_trailer_item(arg_tok);
+		break;
+	case EXISTS_REPLACE:
+		add_arg_to_input_list(on_tok, arg_tok,
+				      in_tok_first, in_tok_last);
+		remove_from_list(in_tok, in_tok_first, in_tok_last);
+		free_trailer_item(in_tok);
+		break;
+	case EXISTS_ADD:
+		add_arg_to_input_list(on_tok, arg_tok,
+				      in_tok_first, in_tok_last);
+		break;
+	case EXISTS_ADD_IF_DIFFERENT:
+		if (check_if_different(in_tok, arg_tok, 1))
+			add_arg_to_input_list(on_tok, arg_tok,
+					      in_tok_first, in_tok_last);
+		else
+			free_trailer_item(arg_tok);
+		break;
+	case EXISTS_ADD_IF_DIFFERENT_NEIGHBOR:
+		if (check_if_different(on_tok, arg_tok, 0))
+			add_arg_to_input_list(on_tok, arg_tok,
+					      in_tok_first, in_tok_last);
+		else
+			free_trailer_item(arg_tok);
+		break;
+	}
+}
+
+static void apply_arg_if_missing(struct trailer_item **in_tok_first,
+				 struct trailer_item **in_tok_last,
+				 struct trailer_item *arg_tok)
+{
+	struct trailer_item **in_tok;
+	enum action_where where;
+
+	switch (arg_tok->conf.if_missing) {
+	case MISSING_DO_NOTHING:
+		free_trailer_item(arg_tok);
+		break;
+	case MISSING_ADD:
+		where = arg_tok->conf.where;
+		in_tok = after_or_end(where) ? in_tok_last : in_tok_first;
+		if (*in_tok) {
+			add_arg_to_input_list(*in_tok, arg_tok,
+					      in_tok_first, in_tok_last);
+		} else {
+			*in_tok_first = arg_tok;
+			*in_tok_last = arg_tok;
+		}
+		break;
+	}
+}
+
+static int find_same_and_apply_arg(struct trailer_item **in_tok_first,
+				   struct trailer_item **in_tok_last,
+				   struct trailer_item *arg_tok)
+{
+	struct trailer_item *in_tok;
+	struct trailer_item *on_tok;
+	struct trailer_item *following_tok;
+
+	enum action_where where = arg_tok->conf.where;
+	int middle = (where == WHERE_AFTER) || (where == WHERE_BEFORE);
+	int backwards = after_or_end(where);
+	struct trailer_item *start_tok = backwards ? *in_tok_last : *in_tok_first;
+
+	for (in_tok = start_tok; in_tok; in_tok = following_tok) {
+		following_tok = backwards ? in_tok->previous : in_tok->next;
+		if (!same_token(in_tok, arg_tok))
+			continue;
+		on_tok = middle ? in_tok : start_tok;
+		apply_arg_if_exists(in_tok, arg_tok, on_tok,
+				    in_tok_first, in_tok_last);
+		return 1;
+	}
+	return 0;
+}
+
+static void process_trailers_lists(struct trailer_item **in_tok_first,
+				   struct trailer_item **in_tok_last,
+				   struct trailer_item **arg_tok_first)
+{
+	struct trailer_item *arg_tok;
+	struct trailer_item *next_arg;
+
+	if (!*arg_tok_first)
+		return;
+
+	for (arg_tok = *arg_tok_first; arg_tok; arg_tok = next_arg) {
+		int applied = 0;
+
+		next_arg = arg_tok->next;
+		remove_from_list(arg_tok, arg_tok_first, NULL);
+
+		applied = find_same_and_apply_arg(in_tok_first,
+						  in_tok_last,
+						  arg_tok);
+
+		if (!applied)
+			apply_arg_if_missing(in_tok_first,
+					     in_tok_last,
+					     arg_tok);
+	}
+}